Current research on the cell surface membrane is based on the premise that the cell must communicate with its microenvironment and adjacent cells, and that such communication influences a cells' behavior, its role in the organization of a tissue, and its ability to fulfill its destined functions. We propose to study these possible funtions of a cell surface membrane by examining intestinal epithelial cells. Methods have been established using rat intestine to obtain isolated epithelial cells as a crypt to villus gradient. Furthermore, intestinal plasma membranes have been partially purified and separated from a Golgi fraction. We will utilize these techniques to 1) characterize the intracellular pathways of intestinal villus cell membrane glycoprotein synthesis, 2) describe the differences in these membrane glycoproteins in association with cell turnover, differentiation and among the different parts of the intestine, 3) extend our studies on the significance of glycosyltransferases being detected on the plasma membrane, 4) characterize calcium uptake by the partially purified membrane vesicles as a function of a vitamin D dependent membrane function possibly related to membrane synthesis, and 5) determine the changes in intestinal cell plasma membrane glycoproteins in animal models of human diseases where these changes might be suspected as playing a role in an abnormally functioning intestine. These studies will use the intestine as a model tissue with which to define the molecular mechanisms by which the cell membrane contributes to the organization of a cell within the restrictions and metabolic requirements of its tissue structure and function. These studies should also define the role of the plasma membrane in the pathogenesis and pathophysiology of intestinal diseases.